1. Field of the Invention
The present invention relates to a semiconductor manufacturing technology in which predetermined treatment is performed to a semiconductor substrate, including a process of forming a layer of some specified composition on a surface of the semiconductor substrate by means of CVD (Chemical Vapor Deposition).
2. Description of the Prior Art
&lt;Arrangement of Prior Art Semiconductor Manufacturing Apparatus&gt;
FIG. 16 is a front sectional view showing a face-down type atmospheric pressure CVD apparatus of an exemplary semiconductor manufacturing apparatus in the prior art. A reaction container 1 has a reaction container body 2 and a disk-shaped turn table 3, and the turn table 3 is rotatably supposed by the reaction container body 2 through a rotation bearing 4, with its major surfaces retained horizontal. The turn table 3 is fixed at its center to a first end of a cylindrical vacuum conduit 5. Since a second end of the vacuum conduit 5 is fixed to a substrate holder 7, the substrate holder 7 is hung by the vacuum conduit 5 from the turn table 3 within a reaction chamber 5 in the reaction container 1. The turn table 3 is rotated by a driving mechanism not shown, and as it rotates, the substrate holder 7 is accordingly rotated. The substrate holder 7 has a stage 10 and a heater 9 which are fixed to each other on their respective junction planes. A vacuum pocket 13 is formed in a bottom surface of the stage 10 to hold a semiconductor substrate 8 in vacuum suction, and the bottom surface of the stage 10 works as a semiconductor substrate holding surface 11. The vacuum pocket 13 is brought to a vacuum by air exhaustion through the vacuum conduit 5 connected to a suction inlet of a vacuum pump 15, and the semiconductor substrate 8 is held on the substrate holding surface 11 by suction force, with its obverse major treatment surface faced down. Facing the major treatment surface, a reactive gas feed plate 16 is mounted, and reactive gas feed holes are formed in the reactive gas feed plate 16. On the opposite side of the reactive gas feed plate 16 to the reaction chamber 6, there is a reactive gas mixing chamber 19. The reactive gas mixing chamber 19 is provided with a reactive gas inlet hole 20 connected to a reactive gas feeder 21 through a supply conduit. The reaction container body 2 has an evacuation passage 18 conducting the reaction chamber 6 to the outside and an inert gas inlet hole 22 supplying inert gas such as nitrogen gas in an upper portion of the reaction container body 2 at a higher position than the stage 10 of the substrate holder 7. The inert gas inlet hole 22 is connected to an inert gas feeder 23 through a feed pipe.
&lt;Operation of the Prior Art Semiconductor Manufacturing Apparatus&gt;
Operation of the prior art apparatus will now be described. First, the semiconductor substrate 8 to be directed to treatment is conveyed from the outside to the reaction chamber 6 through a conveyance passage. Then, the vacuum pump 15 starts exhaustion so that the semiconductor substrate 8 is held on the substrate holding surface 11 by suction force. In such a state, reactive gases are supplied from the reactive gas feeder 21 through the reactive gas inlet hole 20 into the reactive gas mixing chamber 19. Reactive gas mixture 31 mixed in the reactive gas mixing chamber 19 passes through the reactive gas feed holes into the reaction chamber 6. Heat generated by the heater 9 is equalized by the stage 10 and conducted uniformly throughout the semiconductor substrate 8. The heat causes thermal reaction of the reactive gas mixture 31, and a film of a specific composition is formed on the major treatment surface of the semiconductor substrate 8. Exhausted gas containing the residual gas after the reaction is continuously evacuated from the reaction chamber 6 through the evacuation passage 18.
While the film is formed, the turn table 3 is rotated at a specified rotation speed. This allows the film to grow on the semiconductor substrate 8 uniformly throughout the major treatment surface. Also during formation of the film, inert gas such as nitrogen gas is supplied from the inert gas feeder 23 through the inert gas inlet hole 22 into the reaction chamber 6. The inert gas passes by the heater 9 and the semiconductor substrate 8 toward the evacuation passage 18. Flow of this inert gas inhibits reaction byproduct from attaching to side walls of the reaction container 1, substrate holder 7, etc.
When the film is formed in a specified thickness on the major treatment surface, the vacuum pump 15 is stopped and the semiconductor substrate 8 is released from the stage 10. After that, the semiconductor substrate 8 is conveyed through the conveyance passage out of the reaction chamber 6. The above mentioned procedure is repeated to conduct the similar treatment to many semiconductor substrates.
&lt;Disadvantage of the Prior Art Apparatus&gt;
In the prior art apparatus as mentioned above, although the inert gas works to let the reaction byproduct useless for the formation of the film go toward the evacuation passage 18 as previously mentioned, such byproduct cannot perfectly be removed; residual byproduct, floating around an outer surface of the stage 10, penetrates between the substrate holding surface 11 and the semiconductor substrate 8 because the vacuum pocket 13 is kept in lower pressure than the reaction chamber 6. FIG. 17 is an enlarged sectional view showing the circumferential side wall of the stage 10 and its vicinity, which schematically depicts how the residual byproduct penetrates. Because of the vacuum suction, the vacuum pocket 13 is kept lower in pressure than the reaction chamber 6. Pressure difference between them enable the reaction byproduct floating around the stage 10 to easily penetrate between the substrate holding surface 11 and the semiconductor substrate 8. Although the inert gas is useful to prevent the reaction byproduct from attaching to the circumferential side wall of the stage 10, the reaction byproduct deposited by continuous treatment to many semiconductor substrates also penetrates between the substrate holding surface 11 and the semiconductor substrate 8. Additionally, as exaggerated in FIG. 17, the semiconductor substrate 8 is, when heated, often distorted. Such thermal distortion results in a gap between the substrate holding surface 11 and a reverse major surface 12 of the semiconductor substrate 8. Thus, the thermal distortion would allow more reaction byproduct to penetrates in the gap.
As the treatment procedure is further repeated to new semiconductor substrates, the reaction byproduct penetrating in the gap is gradually accumulated on the substrate holding surface 11. As a result, cohesiveness of the substrate holding surface 11 with the semiconductor substrate 8 is deteriorated, and strength of holding the semiconductor substrate 8 declines. The reaction byproduct penetrating goes beyond the substrate holding surface 11 and is accumulated on an inner wall of the vacuum conduit 5. Consequently, the vacuum conduit 5 is clogged, and the holding strength to the semiconductor substrate 8 further declines.
As stated above, the prior art apparatus must be stopped at a certain frequency and be cleaned in order to prevent decline of the holding strength beyond a limit, and thus it has the disadvantage of bad operating efficiency. In addition to that, because of deterioration of the holding strength, the semiconductor substrate 8 held on the substrate holding surface 11 is released from it, dropped and destroyed, and thus, there is the disadvantage that the yield is reduced.